Service Def System See Dealer (Beginners Guide)

If you own any new model vehicle that operates on diesel, it most likely has Selective Catalytic Reduction (SCR) technology.

It does not matter if your vehicle is a passenger vehicle like an SUV, a truck, or industrial equipment like a forklift.

If your vehicle has this technology, it runs with Diesel Exhaust Fluid (DEF).

The message ‘Service Def System See Dealer’ is not meant to cause any alarm. It is only a signal that could mean many things. One of these things is that the fluid is almost exhausted. This is common in instances where you have covered a specific mileage or accumulated time.

Service Def System See Dealer Meaning?

‘Service Def System See Dealer’ is a warning signal. This signal alerts the driver that the Diesel Exhaust Fluid is running empty.

Or that the def fluid is contaminated. It is a common mistake for drivers or fuel attendants to fill the def tank with diesel.

If this happens, the message will pop up. The format of the warning signal varies from car model to car model. Either as a message or a warning light.

This warning signal must be treated with urgency. Once it comes on, the first thing you notice is that the speed of your vehicle will drop low.

If your car has a display screen, you will see a message reading, 5 MPH max speed in 50ml.

This means that over the next 50 miles, your vehicle will run at five miles per hour.

If you continue to ignore the service def message, the car will stop altogether.

This only goes to show the importance of the def. In some automobiles, the signal comes up as Service Exhaust Fluid; see dealer. Both messages refer to the same thing.

How Often Do You Service Def System?

How often you need to service your def system depends on how much def the automobile consumes per mile.

It could also depend on whether the truck is a heavy-duty or medium-duty model. For example, most heavy-duty trucks consume two percent of def for every gallon of diesel.

Ten gallons of def will carry them through about 8000 – 10000 miles for most trucks. How the indicator turns on also varies from truck to truck.

For example, a Dodge Ram has a gauge that tells the amount of def left in the tank. Ford trucks, on the other hand, have a simple light indicator.

Servicing the def system of a vehicle goes beyond filling up the def tank. It also involves cleaning and replacing the def pump filter.

This filter is found inside the tank. But on larger industrial vehicles, there might also be an external filter.

It is advisable to replace the filter every 1000-2000 hour interval. It is best to check the owners’ manual to know the appropriate cleaning interval for your vehicle.

Performing this service can ensure that the engine functions excellently. 

The activities involved in cleaning the def tank begin with emptying the tank of old fluid.

The next step is to remove any sediment and replace the old fluid with a new supply.

Even though this seems relatively simple, it is essential to allow professionals to handle your servicing. These experts also know how to dispose of the old fluid.

It is best to check the def gauge often to prevent being left stranded.

Especially because def cannot be purchased easily in just any store, it is usually sold in truck stations where expert attendants or dealers help ensure everything goes smoothly.

These attendants know the right processes and can help avoid mistakes like def contamination.

The def tank is well labeled to avoid making the mistake of contamination. The cap of a def tank is blue, compared to that of the diesel tank, whose tank cap is green.

Also, the mouth of the def tank is narrower than that of a regular diesel tank. The standard measurement for the diameter of a def dispensing nozzle is 19mm.

A diesel dispensing nozzle has a diameter of 22mm.

If perchance diesel gets in the diesel tank, do not start the vehicle or try to move it. Doing this will make the fluid flow through the system.

Instead, immediately drain the def tank completely. If diesel gets in the def system, it can damage the SCR catalyst. 

This catalyst is expensive to replace, and there is a possibility that the warranty might be expired.

In a reverse scenario where def gets in the diesel tank, drain the tank without moving the truck.

The reason is that def is not compatible with the regular fuel system. Over time, it can lead to corrosion of the fuel system.

Will Disconnecting Battery Reset Def System?

Disconnecting the battery of your vehicle will not reset the Def System. The reason for this is simple.

The DEF system is not purely electrical. It relies on the DEF pump and gauge to determine when the def system will require servicing.

Generally, disconnecting the battery, especially if the vehicle is equipped with a computer, is a no-no. You run a risk of damaging the battery diodes.

It is even more likely to wipe the vehicle’s memory resulting in a loss of learned values.

When it comes to your battery, the best thing to do is to take it to the professionals.

How To Reset Service Def System See Dealer?

You can reset the def system by yourself if you do not want to take it to the dealer. First, you have to refill the def tank.

After filling it, you will need a scan tool or code reader/resetter to erase the message on your dashboard.

The most common and effective reader is the BOSCH Tech 2. You could also use a pocket code reader.

If you are using the BOSCH Tech 2, the steps to erase your def system are as follows:

  • First, turn your car key to the accessory.
  • Connect the resetter. The socket is usually under the steering wheel and is easy to identify. After plugging in, ensure that the sensors are working.
  • Go to Reductant System Data and check for Reductant Level. There are usually three levels written as Sen.1, Sen. 2, and Sen. 3. The three levels will show 100% active if your tank is full. If not, it will read inactive. You should ensure that you are not looking at the page displaying, Reductant Level Sen. 1 C. This second page is used for circuit checks and shows, Ok.
  • Go back to the module setup. Here you will see a prompt reading, Reductant fluid tank level reset. 
  • Push the reset button that changes the warning to none. The def message on the dashboard will clear out.
  • Go back to the Reductant System Data Reset and push the reset button. This action will make the message come up for a while and then clear completely.
  • Turn off the key and disconnect the resetter. The service def message will be cleared when you turn your car back on.

Alternatively, you can use a pocket reader that is simpler to use. First, turn your car key to the accessory and plug in the reader.

Next, press the red button. A prompt will come up reading Reductant Fluid’s general message.

Next, press the erase button and press read again. This time it will read, Zero code. Finally, restart the truck. There will be no more service def messages.

Service Def see Dealer Easy Fix!! Dodge 5500 DIY repair. Step-by-step.

Read More: What Reasons is Your Brake System Warning Light To Come On?


You do not need to worry if your diesel vehicle is new. All diesel vehicles come prefilled with def.

However, it is good practice that every time you service your car, you top up your def as well.

This way, you are sure that you will not be left stranded when you least expect it.

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